Representative materials for which high surface planarity is required include disks of single-crystal silicon, called “silicon wafer” for used in production of semiconductor integrated circuits (IC, LSI). Silicon wafer is required to have surface which is finished to be highly planar in respective steps of lamination and formation of oxide layer and metal layer, in order to give reliable semiconductor junction of various thin film used for formation of circuit in manufacturing process of IC, LSI and the like. In such a polishing finish process, generally, a polishing pad is fixed to a rotatable supporting disk, which is called “platen”, and an object to be processed such as semiconductor wafer is fixed to a polishing head. Relative motions of these generate relative velocity between the platen and polishing head, and polishing operation is executed by continuous supply of a polishing slurry containing abrasive grains onto the polishing pad.
As the polishing characteristics of polishing pad, excellent planarity and surface uniformity of object to be polished, and high polishing rate are demanded. The planarity and surface uniformity of object to be polished may be improved to some extent by increasing the modulus of the polishing layer. As for the polishing rate, it may be improved by increasing the retaining amount of slurry by making a foam containing cells.
As a method for increasing the retaining amount of slurry, the polishing pad per se may be made into hydrophilic, and concrete examples of such a method include: (1) introducing a hydrophilic group such as a hydroxyl group into a matrix material, and (2) mixing a matrix material and a hydrophilic substance. For example, there is disclosed a composition for polishing pad comprising (A) cross-linked elastomer, and (B) substance having a functional group such as a hydroxyl group (Patent document 1). Also disclosed is a polishing tool in which a hydrophilic substance is added to a material constituting the polishing tool, or a polishing tool attached (modified) with a hydrophilic group (Patent document 2). Also disclosed is a polishing pad formed of thermosetting polymer matrix resin containing a sheet-like substance which is hydrophilic and substantially insoluble in water (Patent document 3). Also disclosed is a polishing pad formed of polyurethane composition containing a urethane resin in which a compound having hydrophilic group is copolymerized, and a hydrophilizing agent (Patent document 4).
However, in the method of (1), when the matrix material is polyurethane, a hydrophilic group such as a hydroxyl group containing active hydrogen will react with an isocyanate group during synthesis of polyurethane, so that an unreacted polyol component may remain in the material. This remaining polyol may provide plasticizing effect, which may cause deterioration in the property of the polishing pad. Further, in the method of (2), it is difficult to uniformly mix the hydrophilic substance into the matrix material, and hence a polishing pad having uniform property cannot be obtained.
On the other hand, when the polishing rate changes before completion of use from directly after starting of use, the polishing condition should be adjusted, which leads the problem of poor polishing efficiency.
For example, there is a disclosure about a polishing material formed of a polishing material composition comprising an isocyanate-terminated urethane polymer and an active hydrogen containing compound wherein the isocyanate-terminated urethane polymer uses aromatic diisocyanate as polyisocyanate, and wherein a lower molecular polyol in the polyol component composed of high-molecular-weight polyol and low-molecular-weight polyol is obtained by using diethyleneglycol, 1,3-butyleneglyocol and the like, with the intention of providing a non-foaming urethane polishing material capable of efficiently polishing a semiconductor wafer and having excellent planarity (Patent document 5).
The polishing material disclosed in Patent document 5 is formed of non-foaming urethane, and such a non-foaming polishing material has a groove formed on the polishing surface because the polishing rate is low. And since abrasive grains in slurry and grinding dusts localize, it is very difficult to stabilize the polishing rate.
Further, a conventional grooved polishing pad has the problem that the groove is clogged with abrasive grains or grinding dusts during polishing, and the polishing rate is decreased with use.
With the intention of increasing the polishing rate, there is disclosed a polishing pad containing a silicone-based surfactant which is copolymer of a polyalkylsiloxane and a polyether having a number of independent cells of 200 to 600 cells/mm2, and an average cell diameter of 30 to 60 μm (Patent document 6). However, the polishing pad disclosed in Patent document 6 has some problem in stability of polishing rate because the groove is susceptible to clogging with abrasive grains or grinding dusts during polishing despite of high polishing rate.    Patent document 1: Japanese Unexamined Patent Publication No. 2002-134445    Patent document 2: Japanese Unexamined Patent Publication No. 2003-11066    Patent document 3: Japanese Unexamined Patent Publication No. 2002-59358    Patent document 4: Japanese Unexamined Patent Publication No. 2003-128910    Patent document 5: Japanese Unexamined Patent Publication No. 2000-17252    Patent document 6: Japanese Patent No. 3455208, specification